The present invention relates to a fabric drawing device for a flat knitting machine, comprising a traction roller, an entrainment means for the latter and rollers pressed against the traction roller. The entrainment means comprises pawls coacting with a ratchet wheel mounted on a traction roller, a tensioning spring associated with the pawls to impart spring bias to the traction wheel, and a cam which acts to increase the spring tension as desired.
This type of embodiment already is known from prior art. The drawing device described in the German patent No. 407,853 uses a cam which operates a lever against the force of a traction spring. The lever supports a pawl which coacts with a ratchet wheel fastened on a roller. The cam follower is prevented from contacting the lower portions of the cam by a tension balance between the force of the spring and the tension of the fabric resisting a downward pull. When the cam acts to increase the spring tension, that is, when the follower passes over a raised portion or protuberance on the cam, the pawl is raised and advances by one tooth. During this period of time, the ratchet wheel is held in its position by a non-return pawl. A certain recoil is then inevitable. This basic principle, which underwent several improvements, still is used. Among other matters, the number of pawls was increased, each of which is of different length in order to subdivide the pitch of the ratchet wheel; fastening points of the adjustable spring were introduced in order to make possible an adjustment of the length and a division of the initial force of the spring; torsion bars were introduced betweed the ratchet wheel and the roller to equalize the transmitted torque, etc.
In conventional drawing means there are substantial fluctuations in the spring tension, thus resulting in variations in fabric tension. These fluctuations often necessitate the inclusion of torsion bars which increase the cost of these mechanisms.
The regularity of the stitches and thus the good quality of the knitted goods is a function of the regularity of the traction exerted on the fabric. Thus, it is understandable that the drawing devices are a subject of continuous research.